1. Field of the Invention
The invention relates to ink jet printers employed with document handling machines and the like and particularly to means for improving the performance of ink jet printers in the environments associated with such machines. The invention relates further to a system for removing dust, bubbles of air, and other contaminants from the head of an ink jet printer and particularly from the orifices and the vicinity of the orifices of such ink jet printers.
2. Description of the Prior Art
Ink jet printers depend for reliability on the maintenance of clean orifices so that droplets of ink can be readily produced as required. In the usual drop on demand configurations for ink jet printers, several orifices are arranged in a pattern and droplets of ink are shot out of selected orifices to produce patterns of dots representing desired characters. In the usual environments in which such jets are employed, wipers are provided which are moved across the openings of the orifices to wipe them clean between times when ink droplets are being produced. The wipers generally operate efficiently in clean environments, chiefly to remove small particles, such as dust, which might otherwise accumulate in and around the orifices.
In the environment to which the present invention has application, large numbers of documents, on the scale of 40,000-100,000 or more per day, are moved along a pathway. In order to align these documents properly so that they may be "read" by character reading machines, they must be moved along in contact with metal guides on the sides and in the bottom of the pathway. Motion along these guides produces wear on the documents which is associated with the formation of dust. After several thousand documents have passed along the path there is a build-up of dust, some of which is picked up by the following documents and by air around those documents and carried to the vicinity of the orifices in the ink jet printer head. Due to a mechanism which is not fully understood, as the documents pass the orifices some of the dust entrained with the documents will strike the orifices where some of it will adhere to surfaces and to ink in and around the orifices. For a time, the wiper will successfully clean off the accumulation of dust and dust mixed with ink. Eventually, however, the wipers will become contaminated with the mixture of ink and dust and some of the mixture will be moved in front of one or more of the orifices obstructing their entrances. The desired ink drops will not then flow properly from the obstructed orifices and characters will be malformed.
Among the prior art devices developed to combat this problem is art disclosed in copending patent application Ser. No. 277,277 in the names of John D. Thomas and Harry L. Wallace, filed of even data herewith, entitled "Method and Apparatus for Eliminating Dust from Ink Jet Printers" and assigned to the same assignee as the present invention. This copending application is hereby incorporated by reference.
The above referenced copending application teaches the use of a preventive method and apparatus which excludes dust from the ink jet head by stirring up the air carrying the dust near the head in such a way that most of the dust is carried past the head and therefore does not contaminate the head. This procedure helps keep the ink jet head and associated orifices clear, however, it has not proven to be completely effective when the document handling machine is run for a substantial period of time. Eventually, if the document handling machine is run for a long enough time without being stopped for cleaning, dust and ink will build up on the wiper and the ink jet head. This mixture of dust and ink forms a kind of paste, or a slurry, which adheres to the wiper and smears across the orifices in such a way that the orifices cannot be wiped clean.
The present invention has been developed to remove dust particles and accumulated mixtures of dust and ink away from the head and the orifices of the jets so that check endorsers and the like will continue to function properly even after thousands of documents have been processed and the associated accumulation of dust and ink dust mixture would otherwise tend to clog orifices of the ink jet.
Another problem associated with ink jet printers is that of air bubbles forming in the jets. In any hydraulic system, air can be a problem. In ink jet printers it is especially irksome, since a tiny bubble can obstruct the passage of ink through a jet orifice or cause drops of ink from the orifice to be deflected from their proper courses. The present invention overcomes this problem of air bubbles in ink jets by purging them from the orifices through application of a vacuum.